[nkaminar]

Brent, the spring force is small compared to the pressure to force the shoes against the drums. The real reason that less pedal pressure is needed is because the friction is helping to force the shoes against the drums. You will have to do a free body diagram of the shoes with all the forces involved to understand how this works. One way to demonstrate this to yourself if to take a pencil and push it against a table with the eraser facing forward. As your increase the angle the force required to move the pencil increases with very little downward effort required on your part. At some angle you will not be able to move the pencil forward. That would be too much self actuating.